Electronic paper (or e-paper) is used for e-reader devices because it only requires power to change the image displayed and does not require continuous power to maintain the display in between. The electronic paper can therefore hold static images or text for long periods of time (e.g. from several minutes to several hours and even several days, months or years in some examples) without requiring significant power (e.g. without any power supply or with minimal power consumption). In contrast, emissive displays which are used for the screens of most other portable computing devices (e.g. smartphones, smart watches, tablet computers, handheld games consoles, portable music players, digital cameras, etc.) require a significant amount of power to maintain an image on the display and the display can, therefore, be a dominant consumer of power in such devices which only have a limited battery life.